GetFormModeTrait.php

<?php

namespace Drupal\se_core\Traits;

use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Entity\Entity\EntityFormDisplay;

trait GetFormModeTrait {

  protected function getFormMode(FormStateInterface $form_state): string {
    $form_display = $form_state->getStorage()['form_display'];
    if ($form_display instanceof EntityFormDisplay) {
      return $form_display->get('mode');
    }

    return '';
  }
}